[PMID 17160701] and [PMID 17081262] or this pdf poster show association between the CHRM2 gene and intelligence . In this study of ~300 Caucasians, the (T;T) genotype appeared to typically have a 4 point higher IQ than the (A;T) genotype, which had a 4 point higher IQ (on average) than the (A;A) genotype. A nearby SNP, rs324640, showed similar results to rs324650, and was in linkage disequilibrium (r2 = 0.90) with it. [PMID 17081262].